ITA 2010 — Questão 15

$\frac{1}{2}\left[\cos\left(\frac{\alpha}{729}\right) - \cos\alpha\right]$

$\frac{1}{2}\left[\sen\left(\frac{\alpha}{243}\right) - \sen\left(\frac{\alpha}{729}\right)\right]$

$\cos\left(\frac{\alpha}{243}\right) - \cos\left(\frac{\alpha}{729}\right)$

$\frac{1}{2}\left[\cos\left(\frac{\alpha}{729}\right) - \cos\left(\frac{\alpha}{243}\right)\right]$

$\cos\left(\frac{\alpha}{729}\right) - \cos\alpha$